


The Cha Eunwoo Theorem

by builtonhope_ (hannadulset)



Category: ASTRO (Band)
Genre: I love astro, I swear, IRL, M/M, OT6, a lot of banter, all night era I guess, binu - Freeform, my fingers just flew on their own
Language: English
Status: Completed
Published: 2019-03-19
Updated: 2019-03-19
Packaged: 2019-11-24 13:07:34
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,503
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18165596
Author URL: https://archiveofourown.org/users/hannadulset/pseuds/builtonhope_
Summary: It always goes like this: Bin sits next to Eunwoo and the rest have to figure out who they sit next to, with a 25% probability of each one ending up next to a particular member. His awful math skills can do that much, at least.Until Eunwoo sits next Jinjin, which expands the equation.Bin hates math. He hates Eunwoo even more.





	The Cha Eunwoo Theorem

**Author's Note:**

> hi I love binu 2death (also the eunwoo thing is intentional and u will see why l8r on) A LOT OF OT6 ACTION BECAUSE I LOVE THEM

It was simple math. Which was ridiculous, because Bin hates math. Unless it was to calculate the change from buying food, which he was glad to say, he've mastered to a T. But, math. 

Bin sits next to Eunwoo, and any one of the remaining four had a 25% probability of sitting next to a particular member. He and Eunwoo are out of the equation, like constants. He remembers that much from a disastrous statistics class. 

Except now, he can't remember what his professor said about constants. Specifically, on whether or not those constants change. Can they become _not_ constants? He stares at the back of Eunwoo's head, which becomes his side profile as he turns to take the seat next to Jinwoo.  He tries not to glare, but his jaw is clenched and Eunwoo's looking resolutely at his seat belt like it was the most fascinating piece of fabric he's ever seen in his life. 

"Hyung," Minhyuk says softly, a hand on the small of his back. "You're holding up the line."

Bin blinks. Eunwoo's still memorizing the checkered pattern of the seatbelt. Minhyuk pushes him gently along. 

He's part of the equation now. What's the probability of him sitting next to Minhyuk instead? He doesn't know. He hates math.

* * *

The seating conundrum doesn't extend to hotel room allocations, thankfully, since their rooms are split up into threes this time. Jinwoo says they should split up according to maknae line and hyung line. Bin nods mutely, then marches to the elevator. Behind him, Minhyuk is pushing off an overeager Sanha, who is trying to cling to his smaller hyung. 

"Yah! Yoon Sanha!" Minhyuk snaps as Sanha wraps both arms around his waist. "Get off, you baby giant!" 

"Rocky-hyung," Sanha whines, as Minhyuk slaps his arms. "You're no fun to cuddle, you're built like a rock. Bin-hyung is even worse." He says Bin's name like a curse, and Bin momentarily forgets he's mad at Eunwoo.

"Say my name properly!"

"What's the purpose of rooming together if your roommates are no fun to cuddle with?" Sanha declares dramatically, throwing his arms out to the side. He nearly hits a decorative vase, and the three of them burst out laughing. 

"Sorry Sanha, I wouldn't trade these-" Minhyuk flexes a defined bicep, "for anything. Not even to cuddle with you." He blows Sanha a kiss, and the two of them start a mock fight. Bin ignores them again as he waits for the elevator to come down.  

His mind is still on the plane, in the way Eunwoo became a non-constant. How the equation expanded to one that Bin can no longer comprehend, both literally and figuratively, in the span of a few seconds. 

Or has it been a long time coming? They've drifted apart since they've changed dorms and Eunwoo's solo schedule became even denser than before, but has Bin underestimated how much? Have they really grown so distant that even their sacred airplane seat arrangement is desecrated? 

"Why can't you be Eunwoo-hyung!" Sanha shrieks as Minhyuk punches his arm. "He's so cuddly, like a bear." 

"Bears aren't cuddly, you idiot. They maul giant babies, like this!" Minhyuk grabs Sanha's wrist and pretends to take a bite. The elevator arrives and the three pile into it, Minhyuk still holding Sanha's wrist.  

Bin stares into the hallway, as the Myungjun signals him to hold the elevator. He can't see his expression from afar, but he knows Eunwoo is looking at him. Sanha is waving enthusiastically at Eunwoo, no doubt wanting to hug his hyung and rub it into MInhyuk's face. It would have been fun to listen to the six of them bicker up to the 28th floor, except-

Except Sanha would be rubbing it into his face too. Suddenly, Bin can't stand it and he presses the elevator shut, Myungjun's angry "Yah!" barely audible as the doors close.

The two turn to him in surprise. "Bin-hyung," Sanha starts, "why is your face all red?"

"You're holding hands! It's making my heart flutter." Bin snaps. Minhyuk lets go of Sanha, who bursts out laughing.

"You might get a heart attack if I do this, hyung!" Sanha exclaims gleefully, taking Minhyuk's face into his hands and planting a sloppy kiss on his cheek. Minhyuk slaps the side of Sanha's head, and the two resume fighting.

Bin stares miserably at the pair, feeling his heart sink to his stomach. Wasn't he and Eunwoo like that, just a couple of months ago?

Just how much had they changed?

* * *

The misery lasts well into the morning, the night having been spent in silence, Bin choosing a solo bed and calling it an early night. Sanha and Minhyuk wrestle on the double bed while he curls up away from them, giant headphones blasting whatever song comes up on shuffle. 

Bin figures someone must've tended to him while he slept, because he woke up with a blanket draped over him and his earphones tucked away neatly on the bedside table. The curtains have been pushed open, letting the morning light stream through. The room was cheerful and bright, very much unlike what he was feeling at the moment. 

"Hyung," Minhyuk is fresh from the shower, one towel wrapped around his slim hips, another drying his hair. "Stop being miserable." 

"I'm not." He replies curtly, standing up and walking over to the other bed. He raises a leg and prods at the lump that is Sanha.

"You are. It's contagious. You're dampening my aura," Minhyuk runs a hand through his damp hair and poses like he's in a high-end photoshoot for Bin. His voice drops a pitch as he says, "I can't be Rocky with a negative aura surrounding me."

"You're a moron." Bin rolls his eyes, continuing to toe Sanha's side. Sanha grabs Bin's legs and clings to it, still half-asleep. 

"No, you're the moron." Minhyuk retorts. "We're all going to get an earful from the stunt you pulled yesterday." 

"What stunt?" Bin wants to punch Minhyuk. Why is this his fault? It was Eunwoo who pulled the stunt, choosing to sit next to Jinwoo and deciding he wouldn't be a constant anymore. It was Eunwoo who made the probability something Bin could no longer calculate. It was his fault.

"Closing the elevator doors on MJ-hyung!" 

"The doors closed by themselves, Minhyuk! That's how elevators work!"

"You pressed close!"

"How would you know? You and Sanha were busy being a living drama!"

Minhyuk scoffs. "This isn't about me and Sanha and you know it."

"Then who is it about?" Bin snaps. Sanha's awake now, his grip on Bin's leg loose, his eyes going back and forth between Minhyuk and Bin.  

Minhyuk narrows his eyes, and ignores the way Bin's hands have curled into fists. "You tell me, hyung."

Bin opens his mouth to retort, but the doorbell chimes just in time. Sanha leaps and runs over to the door. Bin doesn't take his eyes off Minhyuk, who does the same. For a few seconds, the only thing he can hear is his deep breaths and the way his heart pounds in his chest. Then Sanha comes back, with Jinwoo in tow. 

Their leader is smiling, but his eyes look worried. Minhyuk must have noticed too, because he deflates immediately. Bin slowly uncurls his fists.

"Are you guys okay?" Jinwoo asks, using his soft voice, the one he uses to pacify fights or talk members through their anxiety.

"Yeah," Minhyuk mumbles, looking at the ground. "We're fine, Jinjin-hyung."

Jinwoo looks at Bin next, his gaze alarmingly perceptive. Bin tries for a smile and a carefree shrug. "Why would you think we wouldn't be, hyung?"

Jinwoo continues to look at him for a few moments, and he fights the urge to scratch his neck to hide his embarrassment. The silence stretches forever, until Jinwoo nods. "Good. Get dressed. We'll be having breakfast in our room."

Jinwoo turns to leave. Bin walks past Minhyuk and goes into the bathroom. The last thing he hears before he closes the door is Sanha's puzzled, "What's wrong with Bin-hyung?"

He doesn't hear Minhyuk's answer. He doesn't need to, anyway. He already knows what it is.

Or rather, _who._

-

As predicted, he gets an earful from Myungjun. Although it's not as bad as it could have been, because he jokes that he only did it to spare the rest from Minhyuk and Sanha acting all lovey-dovey. Myungjun takes the bait and terrorizes Sanha instead, who is now using Jinwoo as a human shield. Minhyuk's in the corner, playing a game on his phone. Bin's on the floor, the spectacle of Myungjun trying to hit Sanha with his slipper without hurting Jinwoo silly enough to lift his spirits a little.

It also helps that Eunwoo's out to help get the food. He comes back soon enough though, and not even Sanha now piggyback-riding the much smaller Jinwoo can make Bin ignore his presence. 

Eunwoo doesn't meet his eyes as he hands him his box, and Bin only nods in thanks. The room descends into blissful silence as they dig into their breakfast, spats forgotten. Minhyuk hands him a water bottle and Bin opens it, which has become their strange way of apologizing to each other. 

Sanha notices, and he claps happily. "Rocky-hyung and Bin-hyung have made up!" 

"You look like a dumb seal." Myungjun tells him, before turning towards Bin and Minhyuk. "Did you fight? Why?" 

"No." Bin says at the same time Minhyuk goes, "no reason." 

"You can't fight, okay?" Myungjun waves his chopsticks around as he speaks, flinging rice everywhere. Jinwoo dodges a grain, looking disgusted. "You'll ruin binhyuk."

Bin snorts. "Binhyuk is already ruined. I'm too pretty to end up with Minhyuk."

"Yah!" Minhyuk scoots over and slaps Bin's arm with the back of his hand. "I can't be with someone who looks like bread dough when he wakes up! It'll be like sleeping with an unbaked gingerbread man."

"Gingerbread is delicious!" Sanha pipes up unhelpfully. 

"Then I'm the real gingerbread," Jinwoo exclaims, placing his head on his upturned palms. "Because I'm soft and sweet, probably also delicious."

 "He said unbaked gingerbread, you moron. Which means you taste like raw flour and can give everyone food poisoning." Myungjun says, rolling his eyes.

The four continue to bicker, the discussion now delving into yet another variation of why Sanha is a giant. Bin opens his mouth to say something, but stops when he can feel Eunwoo's eyes on him. He turns to see that his knuckles have gone white from gripping his fork, but he isn't saying anything. Bin doesn't either, holding his stare.

Everything fades away, the noise, the room, even the box of food on his lap, until it feels like he and Eunwoo are in a vacuum, existing but only for each other. He feels his face getting warm, but he doesn't break the stare. He's too far away, and it makes Bin want to get up and walk over and-

And then what? What would he say? Admit he's angry and jealous that Eunwoo didn't want to sit next to him on the plane? How preposterous. Especially when it seems like such an insignificant thing. Who gets mad over plane seats? Well, Bin, _obviously_ but it doesn't make it any less wrong.

"Uh, Bin?" Jinwoo says, waving a hand between them. Bin blinks in surprise, then feels his face flush. He checks Eunwoo's face, but he's already gotten up and turned his back on him, fussing over the empty take-out boxes instead.

"Hm?" He says, eliciting a deep sigh from Jinwoo. He takes the box out of Bin's lap and helps him up, before leading him to the hallway. From the corner of his eye, he can see Minhyuk shoot him a concerned glance. 

"Bin," Jinwoo says, and he sounds serious enough that Bin drops the fake smile on his face. "Get it together."

"I will, hyung." He promises, but it sounds hollow to his ears. It must have for Jinwoo too, because he pulls Bin into a hug. 

"Please, Bin. Even just for tonight," he grips him tighter, and guilt washes over Bin. He shouldn't let anything get in the way of Astro doing well, especially since it's been so long since they got to perform. "Get it together."

* * *

In the end, he does get it together. In fact, he's gotten it so together, that when they goofed around and took turns doing "such a goodnight" with each other, he grabs Eunwoo and asks him to do it with him.  

He agrees, but they don't look at each other while they do it and their hands barely make contact with each other's bodies. Still, the crowd goes wild for the soap couple. After, Eunwoo smiles at him briefly and walks away. Jinwoo grabs Bin's hand and squeezes it, while he hopes that everyone is preoccupied by Sanha and Myungjun doing it to notice how much he's trying to hold back his tears. It only lasts for a moment though, and by the time they've launched into their next song, the tears have all been blinked away.

The show ends on a high note, the entire stadium singing You and Me uplifting everyone's spirits. Myungjun is still chanting the chorus as they pile into the elevator, Sanha and Minhyuk joining him in varying pitch. Jinwoo doing beatbox, Eunwoo trying to poke his cheek while he huffs and puffs. Bin feels his chest warm as he watches them goof around, happy that Jinwoo was able to talk some sense into him before the show. He couldn't rob them of this giddiness, of the adrenaline that comes after a great show. Sanha loops an arm around his shoulder and he joins them, purposely singing flat. 

The elevator arrives into their designated floor and the singing mercifully stops. They bid goodnight to each other and he, Sanha and Minhyuk tumble into their room. Bin collapses into his bed, groaning as he stretches his arms above his head. "God, I'm tired!" 

The sheets of the other bed rustle. Bin lifts his head to see Sanha grimacing, rubbing his side. "Oh, uh, hyung," he starts, "Jinjin-hyung said we need to go to their room."

"Why?" He stares at Sanha, confused. He sounds like he's rehearsed his invitation. Beside him, Minhyuk looks like he's holding back laughter. 

"There's, uh, food?" Bin sees Minhyuk's arm dart out and pinch the back of Sanha's leg. "There's food!" He squeaks, nodding vigorously. "Food." 

"I'll pass."  

"They have _galbitang_." Minhyuk says, and Bin darts up. 

" _Galbitang_!" Bin exclaims happily, running past the pair and out onto the hallway. He ignores their bickering and enter the hyungs' room, eyes closed and arms open wide. " _Galbitang_! Come to papa!"

" _Galbitang_?"

It's Eunwoo. He's alone, sitting atop the bed, arms folded across his lap. Bin feels his mouth go dry. They haven't been alone in so long. "Sanha said you had _galbi_."

Eunwoo doesn't say anything. The silence drapes the room like a thick blanket making Bin feel light-headed and suffocated. He backtracks, embarrassed, half-hoping Eunwoo will call out to him. He doesn't, and Bin can already feel the tears pricking up again.

He pinches his leg angrily. Why does he keep wanting to cry in front of Eunwoo? His back hits the door and he scrambles for the knob, desperate to go out.  

Only. 

It. Won't. 

Open. 

"Bin," Eunwoo calls out. It's the first time he's heard him say his name on this trip, and he almost stops twisting the knob but he doesn't. It's even worse now that Bin hears him say his name, because it vaporizes the anger he had for Eunwoo, the feeling of missing his best friend overpowering whatever grudge he had been trying to hold. "Is everything alright?" 

"No!" He lashes out. The knob stops rattling. Sobs fill the room, and Bin is horrified as he realizes that it's him. "It's not fine," he says, heaving. "Not at all."

He feels a hand wrap around his wrist, and he's pulled into Eunwoo's chest. He continues to cry until the light blue front of his sleep shirt turns dark. Eunwoo's rubbing comforting circles into his back, but he can feel his him trembling. At the thought of Eunwoo crying, Bin plants both hands on his chest and pushes him away.

"Why are you crying?" He says, feeling impossibly angry at the way Eunwoo wipes his tears with the back of his hand. Bin wants to do it himself.

"Why are you crying?" Eunwoo retorts in a childish tone, making Bin seethe.

"Because of math!"  

Eunwoo stares at him, red-rimmed eyes narrowed in confusion. "Math?" 

"Yes, math!" Bin stomps his foot in frustration. Why can't Eunwoo just get it? Aren't people always praising him for being smart? "You ruined my probability equation!" 

"Your what?" Now, Eunwoo sounds equally mad. He walks over and shoves Bin's shoulder. "What are you talking about?"

Eunwoo is close enough that Bin can reach over and massage the space between his eyebrows, soothing away his frown. But he stands still, hands clutching the loose fabric of his sweatpants. He doesn't look him in the eye as he says, "We always sit next to each other on the plane." 

Bin waits for Eunwoo to say something. He doesn't, so Bin continues to speak to the scuffed tops of his sneakers. "We always sit next to each other, so we're constants. The equation left is simple enough that even I can do it. Everyone has a 25% chance of sitting next to another member. See?" He lifts his eyes and meets Eunwoo's gaze. His expression is unreadable, but he looks like he understands. "But then you sat next to Jinjin-hyung, Can constants be non-constants? What is the probability if you have six members and three sets of chairs then? I wouldn't know," Bin shakes his head and gives him a weak smile. "I'm bad at math."

"Why is it my fault?" Eunwoo says, sounding so hurt that Bin almost flinches. He runs a hand across his face and takes a deep, shuddering breath. "You pushed me away first." 

"What?" Bin can feel his face heat up again. "How can I push you away when we barely even see each other because you're too busy running around?"

"You keep calling me Eunwoo!" Eunwoo shouts, loud enough that this time Bin does flinch. But he doesn't step back when Eunwoo grabs his hand. "You call Rocky Minhyuk but you never," and his voice sounds quiet, broken almost, "call me Dongmin anymore."

Eun- _Dongmin_  is no longer crying, but Bin steps closer to brush his other hand against his cheek anyway. He rubs a thumb against the top of his cheekbone, never breaking their gaze. He thinks of all the lonely nights he spent alone in their shared dorm while Dongmin was away for filming, sleeping in the bottom bunk because the sheets smell faintly of the soap he uses and a scent that is wholly his own. He thinks of the day they moved into the new dorm, how Jinwoo had pretended not to hear him crying the first night and the morning after, how he told Sanha that they'd been watching a sad movie the night before, which is why his Bin had swollen eyes and yes please, he needs an icepack.

He thinks of the day they drew up the concept for their comeback after months spent in industry purgatory, how manager-nim told them they'd have to cut back on cuddling and kissing each other in public, because their image was to be more refined, more mature. He remembers reaching for Dongmin's hand then, under the table so manager-nim couldn't see it, and giving it a reassuring squeeze. Back then, he had been so sure that their friendship was beyond the skinship they did for fan service. He wasn't entirely sure now. 

"I'm sorry," Bin says, and he feels a fresh wave of tears waiting to spill down his cheeks. "I just- you just grew up so much. You went from minion dork Lee Dongmin to brilliant actor and top model Cha Eunwoo. You were gone for so long that when you came back, I'd forgotten who you were before you left. And then they wanted us to be more mature, which somehow turned to us being cold, and I couldn't imagine Dongmin ever being cold to me so I just saw Eunwoo." He moves his hand away from his face and places it on his waist instead. "I'm sorry."

"Me too," Dongmin's other hand settles on his arm, squeezing it lightly. "I- I don't know how to act around you Bin," he says it like his words are waving a white flag. Bin feels the ground lurch beneath his feet, like he's falling. "I can't stand next to you and not try to put an arm around your waist. I can't pair up with you for games on variety shows and not want to hug you whether we win or lose. I want your voice to be the last one I hear before I sleep. I want to be the one to wake you up. I can't be do things half-baked around you. That's why I have to be cold, because otherwise it'll be too obvious how I want to..." he trails off and suddenly lets go of Bin's hand to wrap both his arms around him. "I just want to be your best friend again, Binnie." 

At the sound of his old nickname, the one Dongmin hasn't said in so long, Bin breaks down into tears again. He hugs Dongmin back fiercely, burying his face in the slope where his shoulder meets his neck. "You never stopped being my best friend, Minnie."

They stay in each other arms, until Eunwoo pushes him gently away. "We're going to look awful when we take selcas tomorrow. We'll sit next to each other on the plane okay?" He laughs as Bin continues to sob. "Stop crying, Binnie." 

"No. I wanted to do this since forever," Bin blurbs through his tears.  

"Cry?" 

"No," Bin shakes his head and drags an arm across his eyes to stop his tears. He takes a deep breath and places his hands on either side Dongmin's face. "This." He presses his lips against his. Dongmin stiffens, then he sighs and buries his fingers in Bin's hair.

There's no more crying after that.

* * *

It's Jinwoo who finds them the next morning. At first glance, Dongmin seems to be alone, one hand beneath his head, the other curled around a pillow on his chest. Except, Jinwoo observes with increasing alarm, the pillow's platinum blonde hair is sticking out from underneath the blanket. He pokes the pillow, and immediately snatches back his hand when it hisses.

"Yah!" Bin shouts, throwing back the blanket. "That was my eye!"

"You're indecent." Jinwoo says, deadpan. Bin can feel the blood rush to his face as the cold air hits his bare torso, but he refuses to give Jinwoo the satisfaction.

"You almost made me blind, hyung." He whines.

"And you made me wish I was blind," Jinwoo turns and slaps Dongmin on the cheek. "Get up! We're leaving in two hours. And you," he grabs Bin's wrist and pulls him out of the bed. "Come with me. We'll never make it to our flight if I leave you two here alone."

Jinwoo tries to drag him out the door, but Bin plants his feet on the ground and takes a moment to drink in Dongmin's face. His face is narrower now, his cheekbones more hollow, his jawline sharper than it had been when they were both so young, rolling around on the bottom bunk, trying desperately to fit two growing boys into a single bed. Dongmin notices him staring and smiles, his eyes crinkling into crescents and Bin feels a laugh bubble its way up his throat. How silly of him to worry. He's still his Dongmin, even after everything.

"You're both impossible." Jinwoo mutters and Bin blows Eunwoo a kiss, the blush that spreads across his face the last thing he sees before they leave the room.

* * *

 

"I call dibs on Jinjin-hyung!" Sanha shrieks, turning a few heads at the crowded airport. Myungjun whacks him with a magazine he had been reading. Sanha rushes to Jinwoo undeterred, and clings to his arm. "I want a soft body to sleep next to."

Minhyuk clings to Jinjin's other arm and sticks his tongue out at Sanha. "Maknae line, rap line, soap couple."

"Shut up, hyung! Pastel hair line, soap couple, whatever you two are," Sanha gestures vaguely at Myungjun and Minhyuk. "I honestly don't care."

"I'm perfect," Myungjun says matter-of-factly. Sanha snorts, which earns him another couple of whacks on the arm.  

"That's it, you giant brat." He pries Sanha's hands of Jinjin and pulls him toward him. "You sit with me." 

Sanha sulks as Minhyuk gloats, Jinwoo rolling his eyes at their antics. Bin watches them with amusement, their bickering as familiar as any of their songs. Beside him, Dongmin reaches into his bag and tosses Sanha a candy bar.

"Stop frowning. You're ugly enough as it is," he says, but he's smiling widely. Bin almost snakes his hand around his waist, but Jinwoo's shooting them a warning glance. He settles for crossing his arms instead.

"What's the point of being the soap couple if you can't even cuddle in airports," he grumbles under his breath. Dongmin must've heard, because he reaches over to poke Bin's waist.

"You're an even bigger baby than Sanha is."

"I'm your baby," Bin replies. In the distance, he hears Minhyuk choke on his drink. He doesn't turn though, he reserves his gaze for Dongmin.

Dongmin hums in agreement. "It's simple math."

"What is?"

"You and me," Dongmin says. He smiles, and Bin wants to melt into a puddle. "We always add up to a hundred percent. Sometimes we each give 50-50, sometimes you give 70 and I can only give 30, sometimes it's the other way around. But even when you can only give 1, I'd give the other 99 to see you smile."  

The other members are now quiet and looking everywhere but them. "Dongmin, I love-" Jinwoo coughs obnoxiously, Sanha giggles high-pitched, Minhyuk makes a gagging motion, and Myungjun whacks Minhyuk with his magazine. Bin rolls his eyes and starts over. "I love math." 

Dongmin's eyebrows shoot up in surprise. "That was low, Bin!" He punches his arm as the rest burst out laughing. Bin dodges him and pushes Minhyuk onto his path, and all six of them end up racing each other towards the gate. 

Later, when they're all seated, Bin next to Dongmin, nestled in their own world spun from thick travel coats and an airline-issued blanket, he'll hold his hand and tell him he loves him. But for now, as he catches his eyes as they scramble past Jinwoo and he gives Bin his softest smile- he's pretty sure he already knows.

 

**Author's Note:**

> come cry with me on twitter.com/builtonhope_


End file.
